The present invention relates to the field of exhaust air systems for buildings and/or other enclosed areas, and more particularly, to exhaust discharge nozzles configured to be attached to the outlets of exhaust fans, exhaust ducts and/or stacks, and similar exhaust type equipment/devices and are specifically designed to be installed in the outdoor ambient. The device is designed with a constriction at the outlet to accelerate the exhaust effluent at a high velocity into the atmosphere.
The application of discharge nozzles at the exit point of exhaust systems enhances the performance capability with the specific intent of maximizing the exhaust/effluent dispersion into the upper atmosphere of the unwanted contaminated air and/or effluent gases and vapors from buildings, rooms, and other enclosed spaces. They are able to provide a superior alternative to conventional tall exhaust stacks which are costly to construct and are visually unattractive by today's standards. Properly designed nozzles are capable of propelling high velocity plumes of exhaust gases to heights sufficient to prevent stack downwash and disperse the effluent over a large upper atmospheric area so as to avoid exhaust contaminant re-entrainment into building ventilation intake zones.
A further development of the constrictive exhaust nozzle design is the type nozzle that employs the Venturi effect to draw additional ambient air into the primary effluent stream. The venturi type nozzle can further be described as an aspirating, or induction type, as related to conventional technological description for this type nozzle. The additional induced air volume dilutes the primary exhaust gases at/near the nozzle as the combined mixed air volumes are released into the atmosphere. Also, with this exhaust-air mixture volume increase, the discharged gas is expelled at a higher, velocity, achieving a greater plume height. The underlying effect of greater volume at greater discharge velocity is increased effluent momentum, which assists with the effluent disbursement into the atmosphere.
The limitations of the prior art in this field relate primarily to two issues: (1) the performance of the nozzle in a crosswind, (2) adaptability of the nozzle as a retrofit to an existing exhaust system. With regard to the first issue, crosswinds not only affect the external plume height, in accordance with the Briggs equations (see below), but they can also interfere with and limit ambient air entrainment into the nozzle, thereby impairing the performance at the nozzle discharge. Concerning the second issue, prior art induction nozzles are designed to work with specific exhaust inlet diameters and pressures so that a new exhaust fan assembly must usually be purchased along with the nozzle. The aspirating induction nozzle of the present invention, on the other hand, has the dual advantages of maintaining near-optimal performance in crosswinds and being adaptable as a retrofit for many existing exhaust systems.
The current industry test standard, AMCA 260-07, is a static test based on a zero crosswind velocity, which does not reflect the true application of these devices. Therefore, the industry has not yet recognized the effect of crosswind “blow through” that can take place. The present invention addresses that problem. FIG. 6 illustrates the significantly degraded performance of one of the prior art induction nozzles in a crosswind (15 mph), as compared with FIG. 7 showing the substantially unimpaired performance of the present invention in the equivalent crosswind.
The present invention is designed to be installed on an effluent discharge fan or stack, so as to induce ambient air through induction ports to mix with the primary effluent within a nozzle controlled chamber that is protected from ambient influences, such as crosswinds. The outlets of the induction ports interface with the primary effluent outlets in a radial mixing zone grid within the nozzle interior. In the design of a specific nozzle for a given application, the number, size, and configuration of the induction ports can be arranged, based on the diameter and pressure requirements at the nozzle inlet, to achieve the required discharge velocity of the diluted effluent in accordance with ANSI standard Z9.5 2003. The nozzle of this design extends beyond the interior mixing zone through a length sufficient to allow the process of discharge air static regain to achieve a more uniform velocity profile across the nozzle outlet area, thereby optimizing mixing of the nozzle primary discharge with the induced airflow through the outer wind band annulus surrounding the nozzle.
The intra-nozzle radial mixing zone of the present invention has distinct advantages over the prior art of aspirating type nozzles, in which the induced ambient air mixing takes place peripherally at the nozzle outlet, well beyond the protected environment of the nozzle itself. The two principal advantages of intra-nozzle radial mixing, as opposed to extra-nozzle peripheral mixing, are, (1) more uniform mixing of the ambient air and primary effluent across the entire nozzle outlet and, (2) isolation of the mixing zone from disruption by ambient crosswinds.
A second distinguishing feature of the present invention vis-à-vis the prior art is that the multiple induction ports are not interconnected with each other. In the present invention, the induction air port inlets at the nozzle exterior surface are separated from each other, as are the port outlets terminating within the nozzle interior area. The structure of the nozzle assembly forms individual passageways for the induced ambient air to enter only into the intra-nozzle mixing zone. Several prior art designs use a bifurcated frusto-conical nozzle with a “see-through” central passive zone that functions as the inlet for induced air flow. This “see-through” design allows crosswinds to freely “blow through” the nozzle's passive zone instead of entering the aspiration air column and mixing with the primary exhaust discharge (as depicted in FIG. 6). Such crosswind pass-through impairs the performance of the nozzle by diminishing effluent dilution and reducing the nozzle discharge volume, thereby also reducing plume height.
A third distinguishing feature of the present invention is the extension of the nozzle beyond the mixing zone to create a “developing zone,” in which static regain occurs downstream of the radial mixing zone, within the protection of the nozzle from external crosswind influences. The static regain process converts velocity pressure to static pressure, so as to increase the static pressure of the mixed air column at the nozzle discharge, thereby increasing its motive force for greater plume lift. The static regain that occurs in the developing zone also produces a more uniform cross-nozzle flow velocity profile, which helps integrate the converging air columns from the nozzle and the wind band.
A fourth distinguishing feature of the present invention is a frusto-conical full-length wind band, completely encompassing the nozzle, which extends from or below the induction port inlet level to beyond the nozzle discharge outlet. This has the advantages of (1) protecting the induction port inlets and mixing zone from crosswind disruption, and (2) preventing noise breakout from the nozzle. The full-length wind band also creates an induction annulus between the wind band and the nozzle, thereby setting up a laminar outer aspirated ambient air column surrounding the semi-turbulent inner diluted primary effluent air column. This latter feature increases plume height by both increasing the volume rate of discharge and reducing turbulent energy losses across the outer air column boundary. Several other prior art designs offer only nominal windband protection at the nozzle discharge opening, and the consequent exposure to crosswind influence at the nozzle discharge can cause deterioration of plume height performance with “blow through” across the discharge area.
A fifth distinguishing feature of the present invention comprises one or more short frusto-conical guide vane(s) band in axial annular spaced relation between the lower end of the wind band and the nozzle. The guide vane(s) direct(s) ambient air vertically into the induction ports and block(s) horizontal wind components that would disrupt the mixing zone. The guide vane(s) also work(s) in tandem with the wind band to limit noise breakout at the nozzle entry area. The guide vane(s) thereby contribute to the protection of the entire ambient air entry area surrounding the nozzle against crosswind disruption.
A sixth distinguishing feature of the present invention comprises full-length mounting brackets positioned at the nozzle exterior, between the nozzle and the wind band, wherein the brackets form individual vertical air passageways for each of the ambient air induction ports and maintain the wind band and guide vane(s) in annular spaced relation to minimize crosswind effects, which could otherwise circumvent and disrupt the intended vertical air flow direction.
The mounting arrangement of the induction ports within the nozzle of the present invention also allows for readily attaching, within the nozzle interior, integral sound attenuating material, without reconfiguring the nozzle exterior profile or significantly increasing nozzle static pressure losses at the primary air passageway. The intent of adding this material is to assist with attenuating sound generated by any air flow moving equipment located at the primary air entry end of the nozzle. The nozzle design also readily accepts additional traditional attenuation devices, if needed, that could be located at the nozzle entry point.
The forgoing features and their associated functions have not been achieved by the prior art in this field. With the present invention, each of these above described components function individually, and cooperatively, to assist in the induction of ambient air into the primary air stream for the purpose of maximizing effluent plume height and dilution with minimum interference from ambient crosswind, as shown in FIG. 7. On the other hand, performance modeling of several prior art designs indicates that plume height and dilution performance can be diminished by as much as 40% in a 15 mile-per-hour crosswind, as illustrated in FIG. 6.
The U.S. patent of Cash (U.S. Pat. No. 3,719,032) describes multiple nested venturi nozzles mounted on top of an effluent stack. Since induced ambient air mixes peripherally with primary effluent above each venturi stage, the Cash device lacks the intra-nozzle radial mixing zone which is the first key feature of the present invention. It also lacks the advantages of the full-length wind band of the present invention.
The U.S. patent of Andrews (U.S. Pat. No. 4,806,076) teaches a bifurcated frusto-conical nozzle with dual arcuate venturi nozzles circumferentially disposed around a central “see-through” passive zone, which is the source of induced ambient air. As in the Cash patent, the mixing of exhaust flows with induced ambient air takes place peripherally above the nozzle outlets. The wind band is not full-length over the nozzles and does not shield the passive zone ambient air inlets from crosswind disruption. Moreover, the interconnected “see-through” induced air inlets are subject to crosswind pass-through, which impairs nozzle performance, as explained above. Guide vanes are also absent in the Andrews design, and the short wind band mounting brackets do not channel air into the induction zone inlets. The U.S. patents to Kupferberg (U.S. Pat. No. 5,439,349) and Secrest et al. (U.S. Pat. No. 6,112,850) are variations of the Andrews bifurcated “see-through” design, with Secrest adding acoustic-silencing wraps around the nozzle exterior.
The U.S. patent of Tetley et al. (U.S. Pat. No. 6,431,974) teaches the Andrews “see-through” design with multiple nested wind band sections in vertically spaced relation over the arcuate nozzle outlets. This configuration sets up a succession of extra-nozzle peripheral mixing zones, as opposed to the single mixing zone of Andrews, Kupferberg and Secrest et al. Andrews' deficiencies with respect to full-length wind band, guide vanes and mounting bracket also apply to Tetley et al.
In the U.S. patent of Hill et al. (U.S. Pat. No. 6,676,503), a multi-lobed aspirating nozzle has exterior induction ports formed by the concave exterior portions of the lobed nozzle. Because the induction ports never penetrate the nozzle wall, as in the present invention, however, the mixing of induced ambient with the exhaust flow still occurs outside of and peripheral to the nozzle lobes. The deficiencies of the Andrews design with respect to the wind band/guide vane/bracket configuration also apply to Hill et al.
The U.S. patent of Sixsmith (U.S. Pat. No. 7,241,214) teaches the multi-lobed aspirating nozzle of Hill et al., with the addition of vertical and horizontal wind-deflecting members. While these members somewhat perform the functions of the guide vanes and bracket of the present invention, in terms of creating vertical channels for the ambient air to enter the induction ports, the ports remain exposed to crosswinds because the wind band does not extend down to the port inlets. And, as with prior art discussed above, mixing of ambient air with effluent continues to take place externally and peripherally to the nozzle outlets.
In the U.S. patent to Selinger et al. (U.S. Pat. No. 7,547,249), there is an explicit recognition (column 2, lines 5-20) of the inefficiency of extra-nozzle peripheral mixing of induced ambient air with primary effluent. Instead of relocating the mixing zone within the nozzle, however, Selinger reconfigures the nozzle outlet in an H shape to increase the size of the peripheral mixing area. While the induction ports are better defined in this configuration, they remain external to the nozzle and their inlets remain exposed to ambient crosswinds.
Therefore, all the prior art aspirating induction nozzles share, in varying degrees, the problem of degraded performance in ambient crosswinds and inefficient mixing of the induced air with the primary exhaust gas. In addition, they all lack the scalability of the present invention, and hence are not adaptable to retrofitting existing fan/stack installations.